Performance of cutting tools and cutting tool life is favorably increased when cutting tools are maintained at lower than ambient temperature during machining. Cryogenic fluids can be used to achieve this result. Cryogenic fluids are commonly stored in cryogenic tanks (Dewar vessels) at elevated pressures as a saturated liquid. When the saturated liquid is transported to the cutting tool, generally via vacuum jacketed piping that may be flexible or rigid, or a combination of flexible and rigid, some of the liquid will change to vapor, resulting in a two phase flow. The vapor is generally referred to as flash, referring to the conversion of the liquid cryogen into vapor. The factors that cause flash are pressure drops, heat leaking into the system, and combinations of these factors. It is difficult to control the flow rate of two phase cryogenic fluid, i.e., liquid mixed with vapor or flash, without having pulsing and hesitations in the flow that can be damaging to tools. This is especially true when the flow rate is low, such as the flow rate that is required for cooling cutting tools.
The performance of cutting tools and cutting performance will be higher if the vapor content of the cryogenic fluid supplied is lower. Cryogen that is 100% liquid quality means that there is no vapor in the supplied fluid. Cryogen that is 100% liquid quality or near 100% is required for maximum efficiency when using cryogen to cool cutting tools. In order to keep the cryogen in its liquid state for as long as possible until the point of delivery at the cutting tool where it will provide the most effective cooling, the cryogen needs to be subcooled.